[modes] Add user extendable rules to obs-rpm-* modes

This functionality is inherited from Mer project sdk-build modes.

Signed-off-by: Juha Kallioinen <juha.kallioinen@jollamobile.com>
[gdb] Output less text when starting gdb from sb2 session

Signed-off-by: Juha Kallioinen <juha.kallioinen@jollamobile.com>
Merge pull request #1 from kaltsi/master

Add Mer user rule extension capability to obs-rpm-* modes, make gdb less noisy